The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
The dehydrogenation of hydrocarbons, involves the breaking of two carbon-hydrogen (C—H) bonds with the simultaneous formation of a hydrogen molecule (H2) and a molecule containing a double carbon-carbon bond (C═C). The double bond is a highly reactive point that permits the use of double bond-containing molecules as intermediates for the production of typical petrochemical products such as polymers. Dehydrogenation reactions that are of significant industrial interest include dehydrogenation of low paraffins (C2-C5 alkanes) to produce corresponding olefins or alkenes, dehydrogenation of C10-C15 linear paraffins to yield linear-alkyl-benzenes and ethyl benzenes that provide starting points for the production of polystyrene plastics.
Dehydrogenation of alkanes to olefins can generally be classified as either oxidative or non-oxidative reactions. Disadvantages associated with oxidative dehydrogenation include high exothermicity and low desired product selectivity and quality. Non-oxidative processes (i.e., direct dehydrogenation or catalytic dehydrogenation) can suffer from the requirement of a continuous heat supply to initiate the endothermic reaction. The temperatures that are required to shift the equilibria favorably to alkene products during direct dehydrogenation can promote rapid deactivation of the catalyst by coking, resulting in the need for frequent catalyst regeneration. These high temperatures can also lead to thermal cracking of the alkanes, which can lead to undesirable non-selective side reactions that result in formation of byproducts.
Dehydrogenation reactions may appear simplistic; their thermodynamic and kinetic characteristics have, nevertheless, contributed to make the development of technologies that allow for a reliable and efficient industrial application, rather complex. Presently, CATOFIN™, Oleflex, STAR and FBH (Fluidized Bed Dehydrogenation) are technologies used industrially to dehydrogenate propane, n-butane, isobutane and isopentane to the corresponding monolefins.
The CATOFIN™ process uses multiple horizontal reactors that are each equipped with a fixed catalyst bed. The CATOFIN™ process includes three main steps: preheating, catalytic dehydrogenation and regeneration of the catalyst (decoking). The dehydrogenation and the regeneration are cyclic, and are designed to run adiabatically with the catalyst on hydrocarbon feed for very short cycles, followed by the regeneration. A key principal of the process is that the consumption of heat during the endothermic dehydrogenation reaction is closely in balance with the heat restored to the bed during the regeneration cycles. In recent years, the CATOFIN™ process has emerged as a competitive production process for propylene and isobutylene due to its higher product selectivity, energy efficiency and low operating cost with the advance of the catalyst.
In any reaction involving a solid catalyst bed, uniform distribution of fluids and uniform fluid flow are crucial to achieving high process efficiency. The state of the art addresses mostly vertical reactors with two phase charge in downward flow.
U.S. Pat. No. 8,734,728 discloses the design of a gas distributor with ring sparger for an ammonia oxidizer (a vertical reactor). The feed inlet is from the center and the oxidizer is a vertical vessel with a catalyst bed. The bed velocities are uniform and are lowered by the distributor, which is designed with computational fluid dynamics (CFD).
U.S. Patent Application Publication 2012/0079938 discloses a radial flow distributor design for a vertical reactor. The ratio of mass flow rates of process gas is kept proportional to the flow areas of flow channels.
U.S. Pat. No. 8,372,354 describes devices and a system that improves fluid mixing and distribution to the underlying catalyst bed of a vertical reactor. The devices and system also offer other advantages such as decreased mixing tray height, easier maintenance, assembly and disassembly.
U.S. Patent Application Publication 2013/0221123 discloses a reactor inlet distributor and a perforated deflector for a vertical reactor. A relation between the diameter of the perforated distributor, the height of the opening of the inlet distributor pipe of the reactor inlet distributor and the outer diameter of the inlet distributor pipe is given.
U.S. Pat. No. 7,032,894 discloses a device for distributing a gas into a monolith bed of a vertical reactor. The distributor consists of a plurality of flow channels stacked in order of decreasing diameter. The flow channels successively split a flow stream into multiple flow streams prior to flow streams entering the monolith bed.
European Patent Application 2075056 discloses a distributor nozzle for a two phase charge to be used in fixed bed reactors, with the aim of increasing the area over which the mixture is dispersed and making its flow rate equal over the whole area of the bed in the reactor.
U.S. Pat. No. 5,298,226 discloses a perforated plate fluid distributor device that provides uniform gas flow in pressure swing, fixed adsorbent bed vessels.
All of the aforementioned references are incorporated by reference in their entireties.
Reactions of fluid starting materials with a fluid oxidant stream over a fixed-bed catalyst are usually carried, out in upright reactors in which the solid catalysts are present as catalyst beds through which the reactants flow axially or radially. In the CATOFIN™ process, the introduction and mixing-in of the hydrocarbon feed, air and steam, generally has to be effected very uniformly over the entire entry area into the catalyst upstream of the catalyst beds, with very little inhomogeneity of the mixture and within a very short time, frequently less than 0.1 seconds, in order to suppress secondary reactions such as flame formation, cracking, soot formation, etc.
These requirements are virtually impossible to realize in the case of vertical axial reactors and can be realized only with great difficulty in radial reactors. Hence, horizontal fixed-bed reactors, i.e. reactors having a horizontal longitudinal axis and generally a cylindrical shape, are better suited to meeting the above requirements of the CATOFIN™ process.
Thus, what is needed is a horizontal reactor and a device placed inside the reactor and/or a reactor feed line or feed port that improve the distribution of hydrocarbon feed over the catalyst bed for CATOFIN™ processes.